Maximum smartphones have an inbuilt call recording feature these days. You just need to tap on the cassette symbol to start the recording. Still, there are phones which does not have this feature in built. For such phones, you can install the ACR app.

: Download the ACR call recording app from the play store.

: Then Follow the instructions from the app and allow all the access to the app as shown in the Image below

Tap it seven times, at which point you should see the message, "You are now a developer!" With that done, tap Settings, About Phone, Developer Options, and then tick USB debugging." Then tap OK to approve the setting change.

Now turn it ON in fastboot mode and unlock the bootloader.

Install a recovery to help you with flashing.

Flash a supporting custom ROM and gapps.

XDA Developers is a great site to help you with the process, support and Custom ROMs.

Check the below video for One click root method that works on many latest devices: